The present invention relates to a scroll type compressor, especially to a scroll type compressor that compresses gas to supply to a fuel cell.
There are compressors of various types, e.g. a screw type compressor, a rotary type compressor and a scroll type compressor. Particularly, the scroll type compressor is small and light, and generates less vibration and less noise. Therefore, the scroll type compressor is widely used for freezing and air-conditioning. The scroll type compressor produces heat in compression cycle. In a prior art as described in Japanese Unexamined Patent Publication No. 8-247056, a cooling chamber is provided around a discharge port to cool discharge gas.
FIG. 7 is a longitudinal cross-sectional view of a conventional scroll type compressor. A housing of the conventional compressor 100 is constituted of a front casing 101, an end plate 102 and a rear casing 103. The end plate 102 is connected to the front casing 101 on the side of a discharge port 104. The rear casing 103 is connected to the front casing 101 on the side of a motor. The discharge port 104 is formed through the center of the end plate 102. A cooling chamber 120 is defined between the front casing 101 and the end plate 102. A fixed scroll wall 105 extends from a fixed scroll base plate 107 of the front casing 101 toward the side of the motor. Meanwhile, one end of a crank shaped drive shaft 109, which is connected to a drive shaft of the motor, is rotatably arranged on the motor side of the rear casing 103. A movable scroll wall 110 extends from a movable scroll base plate 111 toward the side of the discharge port. Compression chambers 106 are defined between the fixed scroll wall 105 and the movable scroll wall 110. A discharge valve 108 separates the compression chambers 106 from the discharge port 104.
As the drive shaft 109 rotates due to rotation of the motor, the movable scroll wall 110 orbits. Gas, such as air, in the compression chambers 106 is radially inwardly moved toward the innermost compression chamber 106 as is compressed. The gas heats in compression cycle. The compressed gas is discharge to the discharge port 104 via the discharge valve 108, then outside the compressor 100.
Cooling water flows into a cooling chamber 120 via a coolant inlet, which is not shown. The cooling chamber 120 is defined in the vicinity of the compression chambers 106 and the discharge port 104. Therefore, the heat generated by compressing the gas in the compression chambers 106 and the heat of the compressed gas in the discharge port 104 conduct to the cooling water. The cooling water, temperature of which rose due to the heat conduction, flows outside the compressor 100 via the communicating passage, which is not shown.
In the conventional scroll type compressor, as shown in FIG. 7, parts of the compression chambers 106 are adjacent to the cooling chamber 120 via the fixed scroll base plate 107. Therefore, the cooling water in the cooling chamber 120 warms the gas just flowed into outermost compression chambers.
Since the temperature of the suction gas has not risen yet, the temperature of the cooling water may be higher than the temperature of the suction gas. Therefore, in the conventional scroll type compressor, the cooling water warms the suction gas in the outermost compression chambers.
As the gas just flowed into the outermost compression chambers is warmed, the temperature of the compressed gas, or the temperature of the discharge gas, rises. As the temperature of the gas increased, density of the gas decreases. Therefore, mass flow of the gas (kg/hour) decreases. Consequently, compression efficiency decreases.
In the use of the discharged gas, predetermined mass of the gas should be ensured for unity time. Since mass of discharge air affects the amount of electricity generated by a fuel cell, for example, when the discharged air is used as an oxidizer, the fuel cell requires predetermined mass of the discharged air. In such a state, increasing a workload of the compressor can ensure enough mass flow of the discharged air. However, increasing the workload of the compressor causes the motor for driving the compressor to become large.
The present invention addresses the above-mentioned problems traceable to a loss of compression efficiency by restraining unwanted heat conduction.
According to the present invention, a scroll type compressor has a housing, a drive shaft, a fixed scroll member, a movable scroll member, a suction port and a discharge port. The drive shaft is rotatably supported by the housing. The fixed scroll member is fixed to the housing. The movable scroll member is accommodated in the housing, and faces the fixed scroll member. The housing and the fixed scroll member define a cooling region. The fixed scroll member and the movable scroll member define a compression region. The gas introduced via the suction port is compressed in the compression region by orbiting the movable scroll member relative to the fixed scroll member by rotation of the drive shaft, and the compressed gas is discharged from the compression region via the discharge port. Heat resistant means is disposed at least between the cooling region and the compression region. Heat resistance of the heat resistant means adjacent to the outermost compression region is greater than that of the heat resistant means adjacent to the innermost compression region.
The greater heat resistance of the outer heat resistant means relative to the heat resistance of the inner heat resistant means inhibits the suction gas from being warmed by coolant, such as cooling water, in the cooling region. Thereby, the temperature of the discharge gas is decreased.
Additionally, the term of the heat resistance in the present invention is a parameter indication the degree how heat is not conducted. Heat resistance is expressed by xcex94T/Q[K/W] where xcex94T is temperature differential between two points, the unit of which is Kelvin, or K. Q is the quantity of heat conduction, the unit of which is watt, or W. In the present invention, heat of the cooling region is conducted to the outermost compression region of the scroll type compressor. In terms of the heat conduction, heat resistance xcex1 is expressed by xcex1xe2x88x92(T1xe2x88x92T2)/Q=xcex4/(xcexxc2x7A) where T1 and T2 are temperature of both inner and outer surfaces of a solid wall, A is a cross section area of the solid wall. xcex4 is the thickness of the solid wall. Q is the quantity of transferred heat. Then, xcex is the heat conductivity.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.